The present invention relates to electroless silver coating of materials and more particularly to the electroless silver coating of diamond grit.
Use of metal coated diamond grit embedded in the abrasive section of resin bonded grinding elements is a well practiced commercial technique for enhancing the grinding operation. A wide variety of metals for coating the diamond grit have been proposed in the art. The following citations propose diamond grit having a coating of silver thereon: U.S. Pat. Nos. 2,411,867; 3,779,727; 3,957,461; 3,528,788; and 3,955,324; British Pat. No. 1,344,237; and German Pat. No. 2,218,932. Note that U.S. Pat. Nos. 4,024,675 and 4,246,006 form aggregates of diamond grit in a metal matrix which includes silver and U.S. Pat. No. 4,239,502 dips diamond or cubic boron nitride in a molten silver/manganese/zirconium brazing alloy.
The foregoing art, which to some degree proposes to provide a silver coated diamond grit, proposes among other techniques a conventional electroless coating technique whether the metal being coated is silver or another metal. The electroless coating or chemical reduction coating technique typically involves the formation of an ammoniacal silver solution which contains a reducing agent. The diamond grit to be coated is added to such solution for the silver to be deposited from the solution onto the surfaces of the diamond grit.
Typical conventional silver coating formulations can be found in U.S. Pat. No. 3,915,718, and in the article "Electroless Deposition of Silver Using Dimethylamine Borane", Plating, February, 1974, and "The Making of Mirrors by the Deposition of Metal on Glass", U.S. Department of Commerce, Bureau of Standards, Circular of the Bureau of Standards, No. 389, issued Jan. 6, 1931. While conventional techniques appear to succeed rather well when applying a coating of silver to glass, metal, or other objects, such techniques do not provide acceptable coatings on diamond grit. In particular, coatings deposited from such conventional formulations, such as the Brashear formula set forth in the Bureau of Standards circular, are of a spongy filamentary character which tends to be spotty on the surface of the grit. Moreover, only a small percentage of the available silver is deposited on the surface of the diamond grit. Thus, there is a need in the art for a simple technique for the electroless coating of diamond grit with silver wherein a substantially uniform, continuous, coherent coating of silver coats the diamond grit.